Population genetics of the Sporothrix splendens complex from Protea L. in South Africa

Ngubane, Nombuso Portia (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Ophiostomatoid fungi consist of a remarkable assemblage of species that are distantly related (Orders Microascales and Ophiostomatales) and that are grouped based on convergent evolution towards arthropod dispersal. Most of these fungi are known as pathogens of trees. An unusual assemblage of species belonging in the genera Knoxdaviesia (Microscales) and Sporothrix (Ophiostomatales) were found within infructescences of Protea species. Thus far three and nine species, respectively have been described from this niche. Although distantly related, these fungi share the same hosts and vectors with some of them more exclusive in their host selection than others. The reasons for preference towards certain hosts and the different levels of exclusivity are unknown, especially in Sporothrix. Also, in contrast to Knoxdaviesia, nothing is known regarding their population genetic structure. In this study we aimed to gain insight into the population genetics of Sporothrix species in the Sporothrix splendens clade. This was done by investigating the population structure of S. africana, S. protearum and S. splendens. In the second chapter the population structure of S. splendens across its entire known distribution range was investigated and compared to its distant relative K. proteae. These fungi share the same host (Protea repens) and vectors (mites and beetles). In the third chapter the aim was to expand on knowledge of the dispersal of Protea-associated ophiostomatoid fungi to include species found in Protea species occurring outside the Core Cape Subregion (CCR). To this end, the population structure of two sister species, S. africana and S. protearum, were investigated in order to ascertain whether gene flow is restricted based on geography or host identity and whether these two similar taxa represented two discrete species. Population genetic structure was assessed using a fast evolving anonymous marker (m128) and the slower evolving beta-tubulin marker. Genetic diversity (haplotype and nucleotide diversity), population differentiation, rates of migration, isolation by distance and the relationship between haplotypes were calculated for both markers. In the case of S. africana and S. protearum, analyses were partitioned to test the effect of geography and that of host identity. The population structure of S. africana, S. protearum and S. splendens were not structured according to geography and, in the case of the former two, neither were they structured according to host identity. These patterns matched those of Knoxdaviesia proteae and K. capensis. Also, much like the Knoxdavesia species from Protea, the Sporothrix species showed high genetic diversity, rates of gene flow and no signal for isolation by distance. In addition, two new species (Sporothrix smangaliso and S. nsini) were discovered in the course of field work and these are described in the forth chapter based on morphology and phylogenetic analyses of data from the ITS, beta-tubulin and calmodulin DNA markers. Results of this study provide strong evidence of convergent evolution between two distantly related fungal genera driven by adaptation to insect dispersal. In addition, they highlight the importance of the role played by long distance dispersers in shaping populations of Sporothrix and Knoxdaviesia within Protea. The discovery of two additional Sporothrix species belonging to two distantly related clades in the genus supports the hypothesis that the Protea niche was independently colonised more than once by members of this genus and that some clades have since experienced radiation such as the S. splendens clade. However, this radiation does not seem to be driven by host relationships or geography, at least for the non-CCR taxa, and warrants further investigation.

AFRIKAANS OPSOMMING: Ophiostomatoid fungi bestaan uit ‘n merkwaardige versameling van spesies wat verlangs verwant is (Ordes Microascales en Ophiostomatales) wat saamgegroepeer is gebaseer op konvergente evolusie vir artropode verspreiding. Meeste van hierdie fungi is bekende patogene van bome. ‘n Ongewone versameling spesies wat behoort aan die genera Knoxdaviesia (Microscales) en Sporothrix (Ophiostomatales) is in die saadkoppe van Protea species gevind. Sover is onderskeidelik vier en nege spesies vanaf hierdie nis beskryf. Alhoewel verlangs verwant, deel hierdie fungi dieselfde gashere en vektore, met sommiges meer eksklusief in hul gasheer seleksie as ander. Die redes vir die voorkeure vir sekere gashere en die verskillende vlakke van eksklusiwiteit is onbekend, veral in Sporothrix. Ook, in kontras met Knoxdaviesia, is niks bekend oor hulle populasie genetiese struktuur nie. In hierdie studie het ons gemik om insig te verkry in die populasie genetika van Sporothrix spesies in die grootste Protea-geassosieerde klade, die Sporothrix splendens klade. Dis is gedoen deur die populasie genetiese struktuur van S. africana, S. protearum en S. splendens te ondersoek. In die eerste hoofstuk het ek die populasie struktuur van S. splendens oor die hele bekende verspreidingsgebied bepaal, en dit vergelyk met dié van sy verlangs verwante K. proteae. Hierdie fungi deel dieselfde gasheer (Protea repens) en vektore (meite, kewers en dalk voëls). In die tweede hoofstuk (Hoofstuk 3) het ek gemik om uit te brei op die kennis oor die verspreiding van Protea-geassosieerde ophiostomatoid fungi deur spesies wat in Protea spesies wat buite die Kaapse Hoof Streek (KHS) voorkom te ondersoek. Om dit te doen is die populasie struktuur van twee susterspesies, S. africana en S. protearum, ondersoek om te bepaal of geenvloei beperk is gebaseer op geografie of gasheer identiteit en of hierdie twee eenderse taksa twee diskrete spesies verteenwoordig. Populasie genetiese struktuur is bepaal deur gebruik te maak van ‘n vinnig evoluerende anonieme merker (m128) en die stadiger evoluerende beta-tubulin merker. Genetiese diversiteit (haplotipe en nukleotiede diversiteit, populasie differensiasie, en tempos van migrasie, isolasie deur afstand en die verwantskap tussen haplotipes is bereken vir beide merkers. In die geval van S. africana en S. protearum, is analises gekomparementaliseer om die effek van geografie en gasheer digtheid te toets. Die populasie struktuur van S. africana, S. protearum en S. splendens is nie gestruktureer volgens geografie nie, en in die geval van die eerste twee, ook nie volgens gasheer identiteit nie. Hierdie patrone het ooreengestem met dié van Knoxdaviesia proteae en K. capensisis. Ook, baie soos die Knoxdavesia spesies vanaf Protea, het die Sporothrix spesies hoë genetiese diversiteit, hoë tempos van geenvloei en geen sein vir isolasie deur afstand geopenbaar nie. Verder is twee nuwe spesies (Sporothrix smangaliso en S. nsini) ontdek in die verloop van veldwerk, en ek beskryf hierdie twee in die derde data hoofstuk (Hoofstuk 4) gebaseer op morfologie en filogenetiese analises van data van die ITS, beta-tubulin en calmodulin DNS merkers. Resultate van hierdie studie verskaf sterk bewys van konvergente evolusie tussen twee verlangs verwante fungus genera gedryf deur aanpassing by insek verspreiding. Verder beklemtoon die resultate die belang van die rol wat langafstand verspreiders speel in die vorming van populasies van Sporothrix en Knoxdaviesia binne Protea. Die ontdekking van twee addisionele Sporothrix spesies wat aan twee verlangs verwante klades in die genus behoort ondersteun die hipotese dat die Protea nis onafhanklik meer as een keer gekoloniseer is deur lede van hierdie genus en dat sommige klades sederdien radiasie ondervind het, soos byvoorbeeld die S. splendens klade. Hierdie radiase blyk egter om nie aangedryf te word deur gasheer verwantskappe of geografie nie, ten minste nie vir die ekstra-KHS nie, en regverdig verdere ondersoek.

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